What does “bathe someone in a glow” mean?

Bathe in a glow simply means to have a favorable light cast on the person. Typically it's worded the other way: "He bathed in her glow" so the passage quoted is an unusual one. However, I believe the intent is that she cast him in a perfect light, i.e. put him up on a pedestal.

"Bathe in the glow of someone" generally means to share undeservedly in someone elses glory or fame, eg 'as a musician Yoko Ono bathed in the glow of John Lennon'.

"whom she bathes in an impossibly perfect glow" - not exactly sure about that usage. From context I would say the author meant "paints in a perfect light" - ie. ignores all their faults and only mentions or remembers the good points.